1. Technical Field
The present invention relates to a device for and a method of converting scanning patterns of a display device and, more particularly, to a device for and a method of converting interlaced scanning into sequential scanning in a display device so as to reproduce stable images on the screen.
2. Background Art
Generally, cathode-ray tube displays ("CRT") direct an electron beam from left to right in a horizontal direction starting from top to bottom of a picture frame so as to produce a visual representation of an image. The process of deflecting an electron beam successively over all points in a given region is known as "scanning" and the image which is visually reproduced in spots or lines on the scanning lines of the CRT screen is called "scanning spot". Scanning is similar to the progression of the line of vision in reading a page of recording media in line-by-line, left-to-right, top-to-bottom dissection and reconstitution of images.
There are known two scanning patterns used to reproduce a visual representation of an image. The first scanning pattern is known as "interlaced" scanning, and the second scanning pattern is known as "sequential" scanning. Sequential scanning is accomplished by increasing the downward rate of travel of the scanning electron beam so that every successive line is sent. An image on the picture tube screen is formed by moving the electron beam back and forth as it scans individual lines successively. The interlaced scanning is accomplished by increasing the downward rate of travel of the scanning electron beam so that every other line is sent, rather every successive line. When the bottom of the image is reached, the electron beam is sent back to the top of the image. Then, the lines that were skipped in the previous scanning are sent, the initial set of scanning lines is assumed to start at the upper left portion of the picture frame, and then every other line is scanned. The field produced is known as the "odd-line" field. When the "odd" field is completed, the beam retraces rapidly to the upper middle portion of the picture frame. From the upper middle portion of the picture frame, the "even-line" field is developed by scanning even set of scanning lines. Interlaced scanning was developed to increase the number of scanning lines as much as possible in order to reduce undesirable flick in the picture and yet remain within the limited frequency band available for transmission.
As large screen CRT displays have become more common, however, visual characteristics such as flicker and blur of a picture have become more noticeable. A number of high quality picture display systems has been developed in an effort to improve the vertical resolution of a picture through the use of sequential line scanning without the need for the improvement or change of existing systems. Many picture display systems such as disclosed in U.S. Pat. No. 5,444,494 for Video Signal System Converting Circuit For Processing Video Signal Having Interlaced Scanning Lines To Produce Video Signal Having Sequential Scanning Lines issued to Yomamoto et al., U.S. Pat. No. 5,049,994 for System For Converting Interlaced Video Signals To Sequential Video Signals issued to Nakamura, U.S. Pat. No. 4,602,273 for Interpolated Progressive-Scan Television Displa With Line-Crawl Artifact Filtration issued to Carlson, and U.S. Pat. No. 4,524,379 for Double Scanning Non-Interlace Television Receiver With Vertical Aperture Correction Circuit issued to Okada et al., have endeavored to improve the picture quality by converting an interlaced scaning video signal into a sequential scanning video signal. However, many display systems still reproduce jagged images on screen primarily because of the reduction of the vertical resolution. As a result, further improvements can still be made.